Aspects of the invention relate to a power semiconductor component including a vertical gate zone, wherein the gate zone is arranged in a trench structure of a semiconductor body. The gate zone has a gate electrode and a gate oxide. In this case, the gate oxide covers the walls of the trench structure. In addition, in the case of the known power semiconductor components including vertical gate zones, a body zone of a first conduction type is arranged between two gate zones, the body zone being adjoined vertically by a drift zone having a second conduction type, which is complementary to the first conduction type. Adjacent to the gate zones and the drift zone, power semiconductor components of this type have floating shielding zones of the first conduction type.
When power semiconductor components of this type are turned off, the voltage across the component rises on account of the ever present leakage inductances of an electronic circuit. The permissible intermediate circuit voltage present in static fashion is significantly exceeded in this case. Such an overvoltage spike is particularly critical in the case of high currents, or high leakage inductances relative to the current. This becomes apparent particularly adversely in the case of IGBT modules (insulated gate bipolar transistor). The turn-off of high currents is particularly problematic in this case, for example in overload situations, such as when starting up electrical appliances or electric motors, or in the case of motor blockades, or in the case of a short circuit in an application, because the current change di/dt and thus the overvoltage spike rise as a result. Further particularly critical cases for known power semiconductor components of the IGBT type are high intermediate circuit voltages such as occur during the decelerating operating mode, for example, because here there is a decrease in the usable voltage reserve with respect to the permissible reverse voltage of the power semiconductor component.
Hitherto, power semiconductor components of this type, as illustrated in FIG. 5, have always been dimensioned with regard to the critical operating case such as, for example, the overvoltage case with the steepest occurring di/dt at the highest intermediate voltage occurring in the application. By virtue of this measure, IGBT power semiconductor components are then turned off in decelerated fashion in such a way that the overvoltage spike still lies in the permissible range. This leads to a slower turn-off and thus to unnecessarily high switching losses in the normal operating mode, in which the decelerated turn-off would not be required at all.
As a result, the driving outlay for known power semiconductor components of this type is in some instances considerable for the customer since significantly more than just a driving transistor and a gate series resistor are required for such driving. For the turn-off from the short-circuit case, another different driving condition than in the normal switching or overload operating mode is usually chosen, which increases the outlay further for the customer. FIGS. 5 and 6 illustrate this problem.
In this respect, FIG. 5 illustrates a schematic cross section through a cell structure of an IGBT power semiconductor component 5 including a vertical gate zone 7 arranged within a trench structure 8 of a power semiconductor chip 23. The power semiconductor chip 23 has a semiconductor body 9 having a top side 31 and an underside 26. The semiconductor body 9 has a field stop zone 24 and a lightly doped semiconductor layer 21, in which a drift path 22 is arranged. The gate zone 7 projects into the drift path 22 and has a gate oxide 11 and a gate electrode 10 identified by G, wherein the gate oxide 11 is arranged on the trench walls 12 of the trench structure 8. A p-conducting body zone 13 is arranged between two gate zones 7, and is electrically connected to a metallic emitter electrode E via a highly doped p+-conducting region 28. The body zone 13 is adjoined vertically by an n−-conducting drift zone 14 leading from an n−n junction with an n-conducting field stop zone 24, which acts as a field stop junction 29, to a further pn junction 25 of a p-conducting layer 30 on the underside of the semiconductor body 9, which constitutes a rear side emitter ER, wherein a collector electrode C of the IGBT is arranged on the underside 26 of the semiconductor body 9. On account of a field punch-through, the correspondingly weakly doped n-conducting field stop region of the substrate can dynamically supply an additional current during turn-off and thus decelerate the rise in the reverse voltage across the component. However, this capability depends greatly on the intermediate circuit voltage currently present, and therefore does not have a sufficiently large production window since the leakage current or the static reverse voltage likewise suffers from the lightly doped field stop region. Furthermore, the cell structure including emitter region, body zone, gate zone and drift path, in the region near the surface of the semiconductor body 9, is surrounded by a floating p-doped shielding zone 15, wherein the shielding zone 15 extends into the semiconductor body 9 deeper than the trench gate structure.
FIG. 6 illustrates an alternative solution for improving the power semiconductor component characteristic in which the trench structure 8 projects into the semiconductor body by its bottom region 17 deeper than the shielding zones 15. In the case of this power semiconductor component 6 of the IGBT type a robust turn-off behavior is achieved by virtue of the fact that the trench bottom 17 is no longer covered by the floating p-doped shielding zones 15. Rather, here use is made of a dynamic avalanche breakdown effect, also called dynamic avalanche, which occurs at the exposed trench bottoms not covered by floating p-doped shielding zones 15.
Even though a robust turn-off behavior is achieved with this construction, the avalanche effect, avalanche multiplication, nevertheless gives rise, directly at the trench bottom 17, to an injection of hot charge carriers into the oxide 11 of the trench bottom 17, which, independently of the thickness of the oxide 11, leads to a change in the turn-on properties over the course of the lifetime of the power semiconductor component 6, which therefore slowly deteriorate.
Although it might be expected from introducing a deeply extending highly doped p+-conducting region 28 in the center of the p-conducting body zone 13 of a cell, as is illustrated in FIG. 5 and FIG. 6, that the dynamic limiting of the reverse voltage across the component, also called “dynamic clamping” behavior, and the switching robustness will likewise be improved, such a p+-type needle 28 in the p-conducting body zone 13 leads to intensified hole discharge in the on-state case, and thus to significantly reduced flooding at the top side, that is to say to significantly increased on-state losses, primarily if the p+-type needle 28 extends deeper than the p-doped body zone 13 (not illustrated).
For these and other reasons there is a need for the present invention.